1. Field of the Invention
The invention relates generally to the field of exploration and production of hydrocarbons from wellbores. More specifically, the present invention relates to a method and apparatus to operate tubing and pipe conveyed downhole tools within a wellbore. Yet even more specifically, the present invention relates to a method and apparatus to operate tubing and pipe conveyed downhole tools within a wellbore further including a wireline secured to the downhole tool. The apparatus and method of the present invention further relates to the ability to sever the wireline such that the severed portion above the incision can be removed from the wellbore in a relatively short amount of time.
2. Description of Related Art
One of the primary uses of the present invention occurs within a wellbore, therefore in describing the present invention, the terms “top” and “above” mean closer to the entrance of the wellbore, whereas the terms “bottom” and “below” mean further from the entrance of the wellbore and therefore closer to the bottom most portion of the wellbore. As illustrated in FIG. 1, downhole operations within a wellbore 5 can comprise a drill string 15 disposed within the wellbore 5 having a downhole tool 16 attached to the bottom end of the drill string 15. A wireline 10 can further be included that provides a way of transmitting data or commands between the downhole too 16 and the surface. The wireline 10 is generally connected to the downhole tool 16 via a cable head 12. To eliminate the time consuming task of threading the wireline 10 through each segment of the drill string 15, a known side entry sub 20 can be included with the drill string 15. Side entry subs 20 are typically integral with the drill string 15 and include an aperture (not shown) through which the wireline 10 can pass from inside of the drill string 15 to its outside. Once outside of the drill string 15, the wireline 10 extends up the wellbore 5 adjacent to the drill string 15 until it exits the wellbore 5. Outside of the wellbore 5 the wireline 10 is generally threaded through a series of sheaves 11 and onto a spool (not shown).
During some emergency situations it may be necessary to isolate the wellbore 5 by activating rams 8 that exist within a blow out preventer 7. As is well known, the pipe rams 8 extend out from the blow out preventer 7 and sealingly contact the outer circumference of the drill string 15 to produce a seal around the drill string 15 thereby isolating the wellbore 5 from the surface. Such emergency situations include gas kicks, blow out conditions, and any event that could cause the well to be out of control. The presence of the wireline 10 between the drill string 15 and the pipe rams 8 however prevents a sufficiently tight seal around the drill string 15 to adequately isolate the wellbore 5. Therefore, before the wellbore 5 can be isolated currently known methods require that the entire length of the wireline 10 be removed from the wellbore 5 before activating the pipe rams 8. Conventionally, when using a traditional prior art side entry sub 20 within a wellbore 5, in order to remove the wireline 10 an upward force is first applied on the wireline 10 to release it from the side entry sub 20. Then more tension is applied to the wireline to release the bottom connection 12 from the toolstring 16. However, since the downhole tool 16 is often thousands of feet below the entrance to the wellbore 5, and can be at depths exceeding 25,000 feet, there may not be sufficient time to extract the entire length of wireline 15 from the wellbore 5 before the well reaches an uncontrollable situation. Alternatively, in some deep and deviated wells it may be impossible to provide sufficient pulling force on the wireline 10 to release it from the toolstring 16. In addition, when using the side entry sub 20 during wireline fishing operations, a weakpoint in the tool string may not exist downhole. Thus the use of an alternative release mechanism at the side entry sub 20 is desired to reduce risks to an oil rig if an oil well cannot be controlled.
Thus in some extreme situations it may be necessary to activate the shear rams within a blow out preventer (not shown) to isolate the well before a blow out occurs. As is well known, shear rams can shear any object located within the annulus of the blow out preventer 7, including the drill string 15 and the wireline 10. Once the shear pipe rams have been activated, the toolstring 16, drillstring 15, and wireline 10, will probably be permanently lost downhole. This generally permanently damages the well such that it cannot be recovered. Any failure of the shear rams may also result in loss of a rig and significant risk to operational personnel at the wellsite. Therefore, there exists a need for the ability to quickly remove wireline 10 residing within a blow out preventer 7, where the wireline 10 hinders the use of the less destructive, pipe rams to isolate the well.